Sulfones have the general structure RR'SO.sub.2. Sulfones can be produced from a variety of precursors. By way of example, sulfones can be prepared by (a) oxidizing sulphides, (b) rearranging sulphinate esters, (c) adding sulfonyl halides to alkenes and acetylenes, (d) adding sulphinic acids to polarized bonds, and (e) adding SO.sub.2 to polyenes (See. e.g., Durst, T., in Comprehensive Organic Chemistry: Chapter 11.6, Barton and Ollis, Eds., Pergammon Press, Oxford, 1979).
A particular class of sulfones, 2-(alkylsulfonyl)-5-(trifluoromethyl)-1,3,4-thiadiazoles are intermediates used in the production of herbicides. 2-(methylsulfonyl)-5-(trifluoromethyl)-1,3,4-thiadiazole has been reported to possess antifungal activity (See, U.S. Pat. No. 3,562,284). According to U.S. Pat. No. 3,562,284, 2-(substituted sulfonyl)-5-(trifluoromethyl)-1,3,4-thiadiazoles can be made by oxidizing a corresponding 2-(substituted thio)-5-(trifluoromethyl)-1,3,4-thiadiazole in the presence of an oxidizing agent such as potassium permanganate, hydrogen peroxide or peroxytrifluoroacetic acid. Oxidation takes place in an acidic, aqueous medium that includes acetic acid and methylene chloride as a solvent. Methylene chloride is an undesirable solvent from the standpoint of industrial hygiene and handling. Handling is difficult due to its low boiling point (high vapor pressure). In addition, it contaminates aqueous streams. The sulfone product is isolated using crystallization. The reported yield of the sulfone, based on the starting sulfide, was about 65%.
The use of acetic acid in the presence of water in the process necessarily introduces excess water into the reaction and requires purification of the sulfone using expensive crystallization procedures with resultant low yields. There continues to be a need in the art for a practical, inexpensive process for preparing thiadiazole sulfones in high yield.